Volume control



May 2, 1950 D. R. DE BOISBLANC VOLUME CONTROL Filed Nov. 8, 1948JNVENTOR.

Dv R 7 DE BOISBLANC A TTOR/"VEVS Patented May 2, 1950 VOLUME CONTROLDeslonde R. de Boisblanc, Bartlesville, kla., assignor to PhillipsPetroleum Company, a corporation of Delaware Application November 8,1948, Serial No. 59,008

4 Claims.

This invention relates to a dual control unit embodying a novel shaftconstruction. In another aspect, it relates to a ganged resistance unitembodying a coarse and fine resistance adjustment.

In many electrical devices, it is desirable to provide a resistance orother control unit to which both a coarse and fine resistance adjustmentmay be made. This has customarily been accomplished by using a dualresistance unit having two control knobs for adjusting the respectivecontrol shafts, or alternatively, having one control knob for operatingboth shafts. In the latter case, the single control knob turns bothshafts to obtain a coarse adjustment. In order to obtain a fineadjustment, the knob is either pulled out or pushed in, therebyactuating a clutch which disconnects one of the shafts from the knob.

In many types of electrical apparatus, and particularly in detonationmeters, it is very desirable that one control knob be provided but thatno independent adjustment be necessary to transfer the control from acoarse adjustment to a fine adjustment. In such apparatus, the use oftwo knobs is very confusing to the operator who is usually skilled intesting internal combustion engines but not in the operation ofelectrical apparatus. For the same reason, the necessity of pulling outor pushing in the control knob to obtain a fine adjustment is alsoundesirable in electrical apparatus such as detonation meters.

It is an object of this invention to provide a dual resistance unit inwhich both coarse and fine adjustments may be made without longitudinaldisplacement of the control knob.

It is a further object to provide a fine adjustment for a rheostat,potentiometer, or other electrical resistance unit, which operatesautomatically without any conscious efiort on the part of the operator.Upon overshooting the desired adjustment in either direction the merereversal of direction of the knob automatically changes the device fromcoarse adjustment to fine adjustment.

It is a further object of this invention to provide such a resistanceunit which is simple in construction, rugged, durable, and reliable inoperation.

Various other objects, advantages and features of the invention willbecome apparent from the following detailed description taken inconjunction with the accompanying drawings, in which:

Figure 2 is a sectional view taken along the line 2-2 of Figure 1;

Figure 3 is a view of the control with the parts in disassembledrelation; and

Figure 4 is a schematic circuit diagram illustrating a suitableconnection of my dual resistance unit.

Referring now to the drawings in detail, and particularly to Figure l, Ihave illustrated a dual control unit comprising two variable resistorsI0 and I I which are connected together in any suitable manner. Theresistance units l0 and II have concentric control shafts l5 and i5,respec tively, which protrude from a bushing i1 forming a part of thedual resistance unit. The bushing may be provided with the usual locknuts and washer for attaching the resistance units to a chassis or othersupport.

In accordance with my invention, a lost motion driving connection isprovided between the inner control shaft l5 and the outer control shaftl6 whereby both shafts are rotatable as a unit for making coarseadjustments of resistance and one of said shafts is rotatableindependently to a limited extent for making fine adjustments ofresistance. In this connection, it will be understood that theresistance unit associated with the independently rotatable shaft has asub-- stantially lower ohmic value than the other re- Figure 1 is anelevational view of the improved dual resistance unit;

sistance unit.

In the particular embodiment shown, the lost motion connection includesa driving member or pin 2| firmly secured within a diametricallyextending passage or hole drilled through the inner shaft IS. The endportions of the pin are received within openings 24 in the outer shaftI5, these openings being of substantially larger size than the pin 2|.The openings 24 may be conveniently formed by drilling a circularpassage through the outer shaft ii of larger diameter than the pin 2|.

It will be apparent that the inner shaft is rotatable, to a limitedextent, independently of the outer shaft, such independent rotationoccurring while the pin 2! is positioned within the openings 24.However, when the pin 2i engages the walls defining the openings 24, theshafts are rotatable as a unit and the resistance of both units In andII is simultaneously varied. Assuming that the resistance unitcontrolled by shaft is is of substantially lower ohmic value than theresistance unit controlled by shaft l6, and assuming that the resistanceunits are interconnected, it will be apparent that small angularmovements of the shaft IE will produce fine adjustments in resistancethrough rotation of shaft l5 independently of shaft l6. Larger angularmovements of shaft l5 causes the pin 2| to engage the walls of theopenings 24, thereby adjusting both resistances simultaneously with theresult that a coarse adjustment in resistance is obtained. It will benoted that the novel lost motion connection obviates the necessity forlongitudinal movement of the knob in order to obtain a fine adjustment.

A suitable circuit for interconnecting the resistanc units is shown inFigure 4 wherein the resistance units It and II are interconnected by alead 26 and the terminals of the dual resistance unit thus formed areconnected to input terminals menu 28. The terminal 28 is grounded at 29and the. movable arm of resistance unit it is connected to ground by awire 30. The movable arm of the unit I I is connected to the controlgrid of a tube 3| by a lead 32, the anode and cathode of the tube beingconnected in a suitable amplifier circuit, not shown, and the cathodehaving a meter 33 connected in its circuit. In this figure, resistanceis very small as compared to resistance H. Accordingly, simultaneousoperation of the resistances produces a coarse adjustment of the inputresistance of tube 3| while independent operation of resistance unit Itproduces a fine adjustment of the input resistance, 'both adjustmentsbeing obtainable without the necessity of moving one of theshafts'axially in order to provide a fine adjustment. It will be notedthat, when the shaft is rotated in one direction to a sufiicient extentas to adjust both resistance units simultaneously, rotation of the shaftin the opposite direction automatically brings the fine adjustment intoplay to the extent of the lost motion between the shafts.

It will be apparent that a suitable control knob may be secured to theouter shaft it for varying the resistance of the units IO, M in themanner already described. Alternatively, the inner shaft l may beextended beyond the outer shaft and the control knob attached to theshaft 15. It will also be apparent that the lost motion connection maybe provided by fixing the driving member to outer shaft l6 and providingthe lost motion in the connection between the driving member and innershaft l5. Finally, I do not wish the invention to be limited to the useof a control knob for varying the resistance of the units as otherdevices such as universal joints, gears, and the like may be used torotate the control shafts.

The detailed construction of the dual resistance unit is shown by Figure3, which is a view of a particular dual potentiometer with the parts indisassembled relation. From this figure, it will be seen that resistanceunit ll includes a casing 35 having a cylindrical portion 36 and aflanged portion 31 at the rear of the cylindrical portion 36. Fourradial slots 38 are spaced about the inner edge of the flanged portion31 at intervals of 90 degrees and each slot is of generally rectangularshape, extending radially outward from the inner surface of the flangedportion 31. A pair of stop lugs 39, 40 are formed in the cylindricalportion 36, these lugs protruding radially inward and being closelyspaced about the circumference of cylindrical portion 36. angulardirection, the lugs are positioned substantially half way between two ofthe slots 38. It will be apparent that the stop lugs extendlongitudinally of the cylindrical portion 36 from the flanged portion 31to a position closely spaced to the outer edge ll of the cylindricalportion 36. The cylindrical portion 36 is also shaped to form two setsof connecting lugs, one of which is In an shown at 43. The other set oflugs. not shown, is constructed in the same fashion as set 43 and islocated diametrically opposite the set 43 on the cylindrical portion 36.The lugs-43 are formed integrally with cylindrical portion 35 and, instriking out the lugs, a small slot M is formed at each end of the setof lugs. Each set comprises three lugs 45, 46 and 61 which are ofgenerally rectangular shape, although the corners may be slightlyrounded, if desired. The central lug 8G is preferably slightly longerand wider than the outer lugs 55 and 67, and the metal surfaces 38between each adjacent pair of lugs may be slightly rounded, if desired.

The outer shaft 58, which is hollow and adapted to receive the innershaft 95, carries a rotor generally indicated by reference numeral 49,this rotor being adapted to fit within the casing 35. A disc 53 ofinsulating material is secured to the inner end of the shaft it in anysuitable manner. The disc is preferably made of insulating material suchas Bakelite but other types of insulating materials may be used ifdesired, as those skilled in the art will understand. In the preferredembodiment, a metal contactor is held in abutting relation on the innerside of the disc 58 by lugs 5! which fit into two diametrically opposedslots 52 on the rotor. This contactor serves as a contact plate toconnect the rotor of the resistance unit to a stationary contactterminal. A metal plate 53, preferably of copper, is held against theinner surface of the insulating disc 50 by a pair of diametricallyopposed lugs 54 which are struck from shaft it and are bent over theplate 53,

, thereby holding disc 56 against the end of the shaft, It will be notedthat the plate 53 has an opening 55 formed therein of sufiicient size asto receive the shaft H5. The plate 53 is of generally rectangular shapeand has, at its lower end, three lugs 5B, 5'! and 58, the extreme endsof the lugs 58, 58 being inwardly bent and the extreme end of lug 5?,which is wider and longer than the lugs 56 and 58, being bent in theopposite direction. The space between the bent end portions of lugs 55,58 is occupied by an insulating member integrally formed with andprotruding from the circumference of the insulating disc 50. When therotor is positioned within the casing 35, the outer end of lug 5i isengageable with the stops 39 and G0 to limit the rotary movement ofshaft it.

Spaced from the rotor 39 on shaft is is a circumferential groove 66,this groove being adapted to receive a split ring the to hold the partsof volume control H in assembled relation. When the control isassembled, one or more of the lugs 65, 56, d? is bent over the stator tobe later described, to hold the casing and stator. It will be noted thatshaft it is also drilled to form the openings 24 previously referred toin the description of Figure 2.

The stator of resistance unit ll includes a molded base 6| of insulatingmaterial which is of generally cylindrical configuration and which hasan integral flange I52 formed thereon, the surface 63 of this flangebeing coated with a suitable resistance compound, such as a suspensionof carbon particles, to form a resistance element. The flange 62 issplit, as indicated at 64, to prevent short circuiting of the two endsof the resistance element and one end of this element isconnected by 'aspun-over conductor portion 65 to a terminal 66. This terminal extendsthrough a suitable opening in the base 6| and has its inner endconnected through the member 65 to the caramas bon coating forming theresistance element 88. In similar fashion, a terminal 81 is secured tothe other end of the resistance element 88 through a spun-over contact,not shown.

The base 8| is also molded to form a central cylindrical bushing 88 foraccommodating the shaft I8 and this bushing is adapted to abut thismetal contactor positioned against the outer surface of insulating disc58. A bifurcated contact arm 18 is secured by a rivet 1| to the base 8|and this rivet provides an electrical contact between the contact arm 18and a terminal 13 which extends through a suitable opening in the base,and is secured thereto in any suitable manner. The contact arm 18 isformed from resilient spring material and its arms are disposed inencircling relation about the inner cylindrical bushing 88. Dimples I5,18 are formed in the respective ends of bifurcated contact arm 18 andthese dimples form contact portions which are engageable with the metalcontactor integrally formed with the lugs and 52 on the cuter surface ofinsulating disc 58. This contactor also has a bifurcated contact arm I8in tegrally formed therewith and the outer ends of the forks of contactarm 18 are provided with dimples 18 and 88 which are adapted forresilient engagement with the resistance element 83.- Accordingly, itwill be apparent that the contact arm 18 forms the movable arm of apotentiometer and that this arm is connected with terminal 18 throughbifurcated contact arm 18, the metal contactor integrally formedtherewith, bifurcated contact arm 18, and rivet 1|. Each of theterminals 88, 81 and I3 has a bent portion 82 at right angles to themain part of the contact arm. Preferably and advantageously, this bentportion has a perforation formed therein to which a wire may be attachedand it may also be provided with opposed slots, not shown, to facilitatesoldering of a lead thereto.

Cooperating with the stator 8| is a metal disc 83 which has a centralopening defined by a bushing 84, this opening being of suflicient sizeas to readily accommodate shaft I8. The plate 88 is provided withdiametrically opposed sector members 85, 88 protruding from thecircumferential region thereof and each of these members has a pair oflugs 81, 88 formed. thereon. The plate 88 may be secured to base 8| bybending the lugs 81, 88 over the base or, alternatively, the base may beprovided with suitable projections, not shown, for engaging the members85 and 88. The bushing I1, Figure 1, may be secured to plate 88 in anysuitable manner and the shaft may be held in proper relation thereto bythe split clinch ring 88a. It will be apparent that, when these partsare assembled, a potentiometer is formed, the ends of the resistanceelement being connected to terminals 88, 81 and the movable contactbeing connected to terminals 18. It will also be apparent that theposition of the movable contact may be varied by rotation of the shaftI8. Further, all the parts are securely held in assembled relation andconvenient stop means is provided for preventing rotation of the shaftby greater than a predetermined angular movement.

The resistance unit I8 includes a casing 88 having a cylindrical portion8| and a, disc portlon 82 at the rear of the cylindrical portion 8|. Apair of stop lugs 88, 84 are formed in the cylindrical portion 8|, theselugs protruding inwardly and being closely spaced about thecircumference of cylindrical portion 8|. It will be apparent that thestop lugs extend longitudiq nally of the cylindrical portion 8| from thedisc 82 to a position closely spaced to the outer edge of cylindricalportion 8|. The cylindrical portion 8I is also shaped to form two setsof connecting lugs, one of which is shown at 88. The other set of lugs,not shown, is constructed in the same fashion as set 88 and is locateddiametrically opposite the set 88 on the cylindrical portion 8|. Thelugs 88 are integral with cylindricalportion 8| and, in striking out thelugs, a smallslot 81 is formed at each end of the set 88. Each setcomprises three lugs 88, 88, I88 which are of generally rectangularshape, although the corners may be slightly rounded, if desired. Thecentral lug 88 is preferably slightly longer and wider than the otherlugs 88 and I88, and the metal surfaces between each adjacent pair oflugs may be slightly rounded, if desired.

The inner shaft I5, which is adapted to fit within the tubular outershaft I8, carries a rotor generally indicated by reference numeral I82,this rotor being adapted to fit within the casing 88. A disc I83 ofinsulating material, which is similar to the disc 58, is secured to theinner end of shaft I5 by lugs I84, these lugs being integral with theshaft and being bent over a metal plate I85, preferably formed fromcopper. The plate I85 is of generally square configuration and it has,at its lower end, three lugs I88, I81 and I88. Lugs I88 and I88 are bentoutwardly toward the disc I88 and they abut a sector-like projectionintegrally formed with insulating disc I83. The lug I81 is somewhatlonger and wider than lugs I88 and I88, this lug being bent in op positedirection, as compared to lugs I88 and I88. Accordingly, lug IN isadapted to engage stop lugs 83 and 84 when the rotor is positionedwithin casing 88, thereby to limit the angular movement of shaft I5. Thelugs 88, 88 and I88 are adapted to be bent over a cylindrical portionI88 of a molded stator member I I8 to hold the stator and casing 88 inassembled relation.

The stator II8 has an integral flange III, the surface of which iscoated with a. suitable resistance compound, such as a suspension ofcarbon particles, to form a resistance element. Preferably andadvantageously, the ohmic value of resistance element III issubstantially smaller than the ohmic value of the resistance element 83of unit II. In a preferred embodiment, resistance element III may have avalue of 75,000 ohms while resistance element '83 may have a value of 1megohm. The flange upon which resistance element III is formed is splitat II2 to prevent short circuiting of the adjacent ends of theresistance element, and one end of the element is connected by a rivetII3 to a terminal II4 which extends through a suitable opening formed inthe stator II8. In similar fashion, the other end of resistance elementIII is connected to a terminal 5 through a conductive rivet, not shown.

A central bushing H8 is integrally formed with size to accommodate shaftI5 and a sleeve II8 mounted thereon. The sleeve H8 is locked in positionupon the shaft by a suitable clinch ring, not shown, and its function isto hold the parts of the rotor assembly in proper assembled relation. Abifurcated contact arm I28 is carried by the outer surface of insulatingdisc I83 and the outer end of the forks of this contact arm are providedwith dimples I2I, I22 which are adapted to rub against resistanceelement I I I and form a slidable electrical contact therewith. Thebifurcated arm or contactor I20 is secured to disc I 03 in any suitablemanner and it has a flat conductive portion, not shown, which abuts discI03 and is adapted to be continuously engaged by dimples I23, I24 formedon a bifurcated contact arm I25. The bifurcated arms of member I25encircle the bushing H6 and are formed of resilient material so as tocontinuously engage the previously described contact surface integrallyformed with contactor I20. The member I25 is secured to stator IIO by arivet I26 which is in electrical communication with a terminal I21extending through an opening in the stator H and secured thereto in anysuitable manner. It will be apparent that terminal I2I is in electricalcommunication with contactor I20 through rivet I26, bifurcated contactarm I25 and the contact surface integrally formed with contactor I20 andcarried by disc I03.

A support and clamping ring I29 is mounted between stator H0 and casing35. This ring has a plurality of connecting lugs struck out therefrom,one of which is indicated at I30. The lugs I30 are spaced about theinner edge of ring I29 at intervals of 90 degrees and they are adaptedto fit within the radial slots 39 formed in the flanged portion 31 ofcasing 35, thereby to hold the ring and casing in assembled relation.The ring I29 is also provided with integral shoulders I3I and I32 whichprotrude from the periphery of the ring and have generally sector-likeconfiguration. A pair of lugs I33, I34 are formed on each of theprojections I3I, I32 and these lugs are adapted to be bent into contactwith the stator I09 to hold the ring I29 and stator in assembledrelation. Alternatively, one or more of the lugs 98, 99 and I00 may bebent over the projections I3I and I32 to hold the ring I29 and casing 90in assembled relation.

It will be apparent that, when these parts are assembled, apotentiometer is formed, the ends of resistance element III beingconnected to the respective terminals Ill, H and the movable contactbeing connected to terminal I21. Preferably and advantageously, each ofthe terminals III, H5 and I2! has a bent portion per= pendicular to themain part of the terminal. This bent portion may have a perforationformed therein to which a conductor may be attached, and it may beprovided with opposed slots, not shown, to facilitate soldering of alead thereto. It will be apparent that the position of the movablecontact I02 may be varied by rotation of shaft I5, thereby changing theresistance ratio between the wire connected to lead I21 and the wiresconnected to the respective terminals III and H5. Further, all the partsare securely held in assembled relation and convenient stop means isprovided for preventing rotation of the shaft by greater than apredetermined angular movement.

When the parts of the dual volume control are assembled in the mannerdescribed, and a control knob is attached to shaft I5, for example,small angular movements of shaft I5 will produce fine adjustments inresistance through rotation of shaft I5 independently of shaft I5.Larger angular movements of shaft I5 cause the pin 2I, Figures 1 and 2,to engage the walls of the openings 24, thereby adjusting bothresistances simul taneously to effect a coarse adjustment. It will benoted that, when the shaft is rotated in one direction to a suflicientextent as to adjust both shaft in the opposite direction automaticallybrings the fine adjustment into play to the extent of the lost motionbetween the shafts.

While the invention has been described in connection with a present,preferred embodiment thereof, it is to be understood that thisdescription is illustrative only and is not intended to limit theinvention, the scope of which is defined by the appended claims.

Having described my invention, I claim:

1. A dual resistance unit comprising, in combination, first and secondvariable resistance units. said first unit including a tubular controlshaft, a rotor carried by said shaft, a contact surface and a contactelement carried by said rotor, said surface being electrically connectedto said element, a stator having an opening therein for receiving saidtubular shaft, an arcuate resistance element carried by said stator forengagement by said contact element, a contaci'nr carried by said statorand engageable with said contact surface, three terminals carried bysaid stator connected, respectively, to said contactor and therespective ends of said resistance element, said second unit including ashaft of smaller diameter than said tubular shaft and mountedconcentrically therewith, a second rotor carried by said second shaft, asecond contact surface and a second contact element carried by saidsecond rotor, said surface being electrically con nected to saidelement, a second stator having an opening therein for receiving saidsecond shaft, a second resistance element carried by the second statorfor engagement by the second contact element, one of said resistanceelements being of substantially higher ohmic value than the otherresistance element, a contactor carried by the second stator forengagement with said second contact surface, three terminals carried bysaid second stator and connected, respectively, to said second contactorand the respective ends of said second resistance element, and a lostmotion con-' ncction between said shafts including a driving memberfixed to one of said shafts, the other shaft being shaped to form anopening for receiving said driving member, said opening being sub-=stantially larger than said member whereby said first shaft isindependently rotatable to a limited 'extent when said member ispositioned within by said stator and engageable with said contactsurface, three terminals carried by said stator con nected,respectively, to said contactor and the respective ends of saidresistance element, said second unit including a shaft of smallerdiameter than said tubular shaft and mounted concentrically therewith, asecond rotor carried by said second shaft, a second contact surface anda sec ond contact element carried by said second rotor,

said surface being electrically connected to said element, a secondstator having an opening therein for receiving s'aid second shaft, asecond reresistance units simultaneously, rotation of the sistanceelement carried by the second stator for engagement by the secondcontact element, one of said resistance elements being of substantiallyhigher ohmic value than th other resistance element, a contactor carriedby the second stator for engagement with said second contact surface,three terminals carried by said second stator and connected,respectively, to said second contactor and the respective ends of saidsecond resistance element, and a lost motion connection between saidshafts including a driving pin fixed to the inner control shaft andhaving its ends protruding radially therefrom, the outer shaft havingdiametrically opposed bores therein of larger diameter than said pin forreceiving the protruding ends thereof whereby said inner shaft isindependently rotatable to a limited extent when the protruding ends ofsaid pin are positioned within said bores and both of said shafts arerotatable as a unit when said pin engages the walls defining said bores.

3. A dual resistance unit comprising, in combination, first and secondvariable resistance units, said first unit including a tubular controlshaft, a rotor carried by said shaft, a casing including a cylindricalsection, a pair of stop lugs struck inwardly from said cylindricalsection, a metal plate carried by said rotor, said metal plate having 9.lug struck therefrom which extends radially of said tubular controlshaft and has a bent portion engageable with said stop lugs to limit theangular movement of said tubular control shaft, a contact surface and acontact element carried by said rotor, said surface being electricallyconnected to said element, a stator having an opening therein forreceiving said tubular shaft, an arcuate resistance element carried bysaidstator for engagement by said contact element, a contactor carriedby said stator and engageable with said contact surface, three terminalscarried by said stator connected, respectively, to said contactor andthe respectiv ends of said resistance element, said second unitincluding a shaft of smaller diameter than said tubular shaft andmounted concentrically therewith, a second rotor carried by said secondshaft, a second casing having a cylindrical section, a pair of stop lugsstruck inwardly from said second cylindrical section, a metal platecarried by said second motor, said plate having a radially extendinglug, the end of said lug being bent so as to be engageable with saidstop lugs, thereby to limit the angular movement of said shaft ofsmaller diameter, a second contact surface and a second contact elementcarried by said second rotor, said surface being electrically connectedto said element, a second stator having an opening therein for receivingsaid second shaft, a second resistance element carried by the secondstator for engagement by the second contact element, one of saidresistance elements being of substantially higher ohmic value than theother resistance element, a contactor carried by the second stator forengagement with said second contact surface, three terminals carried bysaid second stator and connected, respectively, to said second contactorand the respective ends of said second resistance element, and a lostmotion connection between said shafts including a driving member fixedto one of said shafts, th other shaft being shaped to form an openingfor receiving said driving member, said opening being substantiallylarger than said member whereby said first shaft is independentlyrotatable to a limited extent when said member is positioned within saidopening and said shafts are rotatable as a unit when said member engagesthe walls defining said opening.

4. A dual resistance unit comprising, in combination, first and secondvariable resistance units, said first unit including a tubular controlshaft, a rotor carried by said shaft, a casing including a cylindricalsection, a pair of stop lugs struck inwardly from said cylindricalsection, a metal plate carried by said rotor, said metal plate having alug struck therefrom which extends radially of said tubular controlshaft and has a bent portion engageable with said stop lugs to limit theangular movement of said tubular control shaft, a contact surface and acontact element carried by said rotor, said surface being electricallyconnected to said element, a stator having an opening therein forreceiving said tubular shaft, an arcuate resistance element carried bysaid stator for engagement by said contact element, a contactor carriedby said stator and engageable with said contact surface, three terminalscarried by said stator connected, respectively, to said contactor andthe respective ends of said resistance element, said second unitincluding a shaft of smaller diameter than said tubular shaft andmounted concentrically therewith, a second rotor carried by said secondshaft, a second casing having a cylindrical section, a pair of stop lugsstruck inwardly from said second cylindrical section, a metal platecarried by said second rotor, said plate having a radiall extending lug,the end of said lug being bent so as to be engageable with said stoplugs, thereby to limit the angular movement of said shaft of smallerdiameter, a second contact surface and a second contact element carriedby said second rotor, said surface being electrically connected to saidelement, a second stator having an opening therein for receiving saidsecond shaft, a second resistance element carried by the second statorfor engagement by th second contact element, one

of said resistance elements being of substantially higher ohmic valuethan the other resistance element, a contactor carried by the secondstator for engagement with said second contact surface, three terminalscarried by said second stator and connected, respectively, to saidsecond contactor and the respective ends of said second resistanceelement, and a lost motion connection between said shafts including adriving pin fixed to the inner control shaft and having its'endsprotruding radially therefrom, the outer shaft having diametricallyopposed bores therein of larger diameter than said pin for receiving theprotruding ends thereof whereby said inner shaft is independentlyrotatable to a limited extent when the protruding ends of said pin arepositioned within said bore and both of said shafts are rotatable as aunit when said pin engages the walls defining said bores.

DESLONDE R. or: BOISBLANC.

REFERENCES CITED The following references are of record in the file ofthis patent:

UNITED STATES PATENTS Number Name Date 1,592,193 Farnsworth July 13,1926 1,654,867 De Laval Jan. 3, 1928 2,277,883 Rich Mar. 31, 19422,401,037 Arvin May 28, 1946 FOREIGN PATENTS Number Country Date 450,238Germany Mar. 27, 1926

